How to search between branches

Hallo to all!
I'm new to this list so I hope I'm not breaking any rule, in that case please tell me.

Imagine a software that has 100 source files and a repository that has one directory for the main trunk and an indefinite number of directory for all the branches, one for each ongoing development thread.
So on the repository there are:
/trunk
/branches/b1
/branches/b1